JPH08143361A - Carbonaceous brick for blast furnace excellent in alkali resistance and its production - Google Patents

Abstract

PURPOSE: To improve an alkali resistance of a carbonaceous brick without damaging strength and thermal characteristics and to elongate a life of a blast furnace. CONSTITUTION: 1-20wt.% Al powder having <=2.5μm average grain size is compounded to a carbon starting material such as synthetic graphite and calcined anthracite, and the mixture is kneaded with an org. binding material and formed, then calcined in a reducing atmosphere containing CO or an inert atmosphere containing nitrogen, and the carbonaceous brink for the blast furnace in which a part of an open hole is packed with a filamental Al2 O3 , AlN crystal and/or aluminum oxide nitride and having <=11% apparent porosity and expansion coefficient of <=3 at alkali resistance test is produced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbonaceous brick for a blast furnace and a method for producing the same. More specifically, it relates to a carbonaceous brick for a blast furnace, which has a low porosity and an excellent alkali resistance, and can improve the life of the blast furnace particularly when used for the lining of the blast furnace structure structure, and a method for producing the same.

[0002]

2. Description of the Related Art In the present steel manufacturing process, the mainstream of hot metal production is smelting reduction of iron ore using a melting furnace (blast furnace). Although the life of this blast furnace has become remarkably long in recent years, progress in the repair technology of blast furnace refractories has greatly contributed to the extension of the life of this blast furnace. As an example, for shaft refractories, life extension technologies such as hot spraying repair of irregularly shaped refractory and replacement of stave cooler have already been established, and the wear of refractory in this part causes blast furnace life. It is no longer the controlling factor.

On the other hand, in the bottom of the blast furnace, hot metal is always pooled, so it is very difficult to directly repair the hot metal. For this reason, up to now, there is no direct repair technology for the furnace bottom refractory, and it is limited to an indirect life prolonging technology that prevents erosion by cooling the refractory through the iron shell, It is desired to develop a refractory material for the hearth, which is more durable.

As the refractory for the hearth, carbonaceous bricks are used.
The use of (block) is the mainstream. This is because carbon has a very high melting point compared to other materials, less deterioration in strength at high temperatures, excellent slag resistance, and good thermal conductivity. This is because it has advantageous high temperature characteristics such as easy cooling through the skin.

Main raw materials of carbonaceous bricks are carbon raw materials such as soil graphite, scaly graphite, roasted anthracite, coke for metallurgy and artificial graphite. Among these, for example, roasted anthracite is excellent in hot metal resistance but inferior in thermal conductivity, while artificial graphite is excellent in thermal conductivity, on the other hand, inferior in hot metal resistance, and bricks made of this are carburized. It is easy to dissolve,
Each has its strengths and weaknesses. For this reason, when designing bricks, only one kind of carbon raw material selected in consideration of necessary characteristics or two or more kinds of carbon raw materials are mixed and used at an appropriate ratio. In the production of carbonaceous bricks, this carbon raw material is kneaded together with an organic binder such as phenol resin or pitch, molded into a predetermined shape by a high pressure press or an extrusion molding method, and then the molded body is fired to obtain a product. Firing
In order to prevent the oxidation of bricks, it is usual to fill the container containing the molded body with coke powder, seal it, and bake it.

[0006]

Although carbonaceous bricks are excellent in high temperature characteristics as described above, they have a drawback that they are inferior in alkali resistance. It is believed that this is because the carbon material, which is the main material, contains oxide components such as Al ₂ O ₃ and SiO ₂ as ash, which are brought into carbonaceous bricks and react with alkalis. . More specifically, in the furnace of the blast furnace, an alkaline component (mainly potassium) derived from a charging raw material such as coke is accumulated with the operation of the blast furnace, and evaporates and solidifies repeatedly to circulate in the furnace. Part of this reaches the bottom of the furnace and penetrates and accumulates in the carbonaceous bricks. The alkali component invading the brick reacts with oxides such as Al ₂ O ₃ and SiO ₂ existing in the carbonaceous brick to form an alkali silicate. Since this reaction is accompanied by volume expansion, it is known that the brick structure cracks and the structure becomes brittle.

Generation of an embrittlement layer due to this alkali (hereinafter,
As a means for preventing alkali embrittlement), it is known to prevent the reaction with alkali by using petroleum coke, coal coke or the like having a low ash content as a carbon raw material (Japanese Patent Laid-Open No. 2006-187242). 59-195580). However, the present inventors prototyped various brick materials, when performing a test to artificially generate alkali embrittlement on bricks in a furnace of an inert atmosphere to which potassium gas was added at various temperatures, containing ash. It was found that alkali embrittlement proceeds at the liquid phase existence temperature of potassium even when a very low amount of high-purity graphite is used as a raw material.

Further, when Al ₂ O ₃ brick was used as a sample by the same test method, it was found that the magnitude of the apparent porosity was in agreement with the degree of embrittlement. That is, Al ₂ O with an apparent porosity of about 13%
_{In the case of 3} bricks, changes peculiar to embrittlement such as swelling, cracking, and peeling were observed, but even with the same composition, in a dense Al ₂ O ₃ ceramic material with an apparent porosity of almost 0%. No occurrence of alkali embrittlement was observed.

From these test results, although the embrittlement of the carbonaceous brick due to the generation of the above-mentioned alkali silicate is one of the factors causing the alkali embrittlement, it is not sufficient to reduce the ash content alone, and it is possible that the embrittlement occurs through the open pores. It was found that preventing alkali from penetrating and accumulating in bricks is necessary to suppress alkali embrittlement.

The reduction of pores in carbonaceous bricks has been studied so far from the viewpoint of preventing hot metal penetration into bricks. Especially in the dismantling of blast furnace,
It is known that the hot metal has penetrated into pores having a size of about μm, and some means for reducing the amount of pores of 1 μm or more in brick have been proposed.

For example, Ironmaking Research No. 331 (1988) p.1-6
For, by adding metal Si in the manufacturing process of carbonaceous bricks, by reacting this with atmospheric gas in the firing process,
It has been proposed to form fibrous crystals of Si-O-N compound in the pores to make the pores fine. According to this method, although the apparent porosity of the brick itself is not reduced, it has been reported that the proportion of pores of 1 μm or less in the total porosity is increased. But applying this method,
When the above-mentioned alkali embrittlement test was carried out on a commercially available graphite-SiC-based brick in which pores were made into pores,
It was confirmed that embrittlement also progressed with this brick. Therefore, in order to suppress the alkali embrittlement, it was found that it is important not only to make the pores smaller, but also to reduce the porosity.

Further, in Japanese Patent Laid-Open No. 172882/1990, for the purpose of improving the oxidation resistance, a carbonaceous brick is impregnated with a solution containing ultrafine metal powder having an average particle size of 1 μm or less. It has been proposed to fill the pores. But,
The carbonaceous block used at the bottom of the large blast furnace is 600 mm x 70
1 μ because it is a large block of 0 mm × 3000 mm
It is doubtful whether even the ultrafine powder of m or less can be impregnated evenly into the center of the block and effectively fill the open pores.

It is an object of the present invention to provide a carbonaceous brick for blast furnace lining, which has suppressed alkali embrittlement and is excellent in alkali resistance, and a method for producing the same. Specifically, the amount of open pores in the carbonaceous brick that causes the embrittlement layer.
It is an object of the present invention to achieve the above object by reducing (porosity).

[0014]

Means for Solving the Problems The present inventors have
As a result of research to solve the problem,
Fine Al powder is added to the material and fired in a specific atmosphere
And the fibrous Al ₂O₃Or AlN generates and this
As a result of filling the open pores, the porosity of the carbonaceous brick is large.
Found that the alkali embrittlement is less likely to occur
Then, the present invention has been reached.

According to the present invention, some of the open pores are filled with fibrous aluminum oxide and / or nitride, the apparent porosity is 11% or less, and the expansion coefficient in the alkali resistance test is 0.5. The following carbonaceous bricks for blast furnace having low porosity and excellent alkali resistance are provided. Here, the expansion coefficient in the alkali resistance test is, as described in detail in Example 1, in the same direction as the molding direction after holding at 600 ° C. for 1 hour in an argon atmosphere containing potassium gas. Means the expansion rate of.

The carbonaceous brick for blast furnace of the present invention is prepared by kneading and molding a mixture containing one or more carbon raw materials, metallic aluminum powder having an average particle size of 25 μm or less, and an organic binder, and then CO ( It can be produced by firing in a reducing atmosphere containing carbon monoxide) or an inert atmosphere containing nitrogen. In a preferred embodiment, the blending amount of the metal aluminum powder is in the range of 0.1 to 20 wt% based on the total amount of the carbon raw material and the metal aluminum powder.

[0017]

The carbonaceous brick of the present invention and the method for producing the same will be described in detail below. The carbon raw material as the main raw material of the carbonaceous block of the present invention, as in the conventional, soil graphite,
It can be selected from scaly graphite, roasted anthracite, artificial graphite, metallurgical coke, etc., but is not limited thereto. It is also possible to use petroleum coke, coal pitch coke, carbon black, etc., which have a lower ash content. 1 carbon source
Species or two or more species can be used. The preferred carbon feedstock is one or both of artificial graphite and roasted anthracite.

The binder serves to bond the carbon raw materials during the molding to enable the molding, and carbonizes during the firing so as to bond the carbon raw material as the aggregate by the carbonized structure generated. Although any organic material capable of exerting this action can be used as the binder, the preferred binder is one or both of a phenolic resin and pitch (eg tar pitch). The compounding amount of the binder is appropriately in the range of 1 to 20 wt% with respect to the carbon raw material as the main raw material.

According to the present invention, metallic aluminum powder (hereinafter referred to as Al powder) is further blended in addition to the carbon raw material and the binder. As the Al powder, fine powder having an average particle size of 25 μm or less is used. Thereby, the porosity of the carbonaceous brick obtained after firing is remarkably reduced, and the alkali resistance is remarkably improved.

Relatively coarse Al having an average particle size exceeding 25 μm
When powder is used, the porosity of the obtained carbonaceous brick is lowered, but the alkali resistance is not sufficiently improved. Further, with coarse Al powder, closed pores are generated inside the brick due to Al evaporation, so that the strength of the obtained brick is significantly reduced. If Si powder is used instead of Al powder, 25
Even if a fine powder having a particle size of less than μm is used, neither the effect of lowering the porosity nor the improvement of alkali resistance can be obtained.

Particularly, when the firing atmosphere after molding is a CO-containing reducing atmosphere, it is preferable to use finer Al powder having an average particle size of 20 μm or less, more preferably 15 μm or less. When the firing atmosphere is an N ₂ -containing inert atmosphere, Al powder having an average particle size of 20 μm or less is preferably used. When the average particle size of the Al powder to be used is too large, the particle size of the Al powder may be reduced so as to satisfy the average particle size specified in the present invention by pulverizing at the time of mixing before molding.

The Al powder content is preferably in the range of 0.1 to 20 wt%, more preferably 0.5 to 5 wt% based on the total weight of the carbon raw material. 0.5 wt% Al powder
% Or less, the reduction in porosity is insufficient. On the other hand, 20wt
If a large amount of Al powder exceeding 100% is blended, the brick may crack due to volume expansion during firing. The purity of the Al powder is not particularly limited, but 95% by weight or more is preferable.

In the manufacturing process of carbonaceous bricks, kneading and molding are performed in the same manner as in the past. That is, the above carbon raw material and Al powder are mixed and pulverized if necessary. An organic binder is added to this mixture, and the mixture is kneaded, aged if necessary, and then pressure-molded into a desired shape by an appropriate means such as a hydraulic press, a hydrostatic press, and extrusion molding. It should be noted that optional additive components other than those described above can be added during powder mixing or kneading as long as the performance of the carbonaceous brick is not significantly adversely affected.
Examples of such optional additives include metal carbide powders such as SiC, metal powders other than Al such as Si powder, and Si
Nitride powder such as ₃ N ₄ may be used.

The obtained molded product is fired after drying. In the present invention, the firing is performed in a CO-containing reducing atmosphere or a nitrogen-containing inert atmosphere. The CO-containing reducing atmosphere includes CO gas alone, or one or more selected from CO and other reducing gases (eg, hydrogen) and inert gases (eg, N ₂ , argon, helium, etc.). The mixed gas atmosphere may be used, and this atmosphere may be circulated around the molded body, or the molded body may be housed in a sealed container having this atmosphere for firing.

Further, as in the prior art, a CO-containing reducing atmosphere can also be generated by filling a compact with a coke powder in a closed firing container.
That is, in this case, since the coke powder reacts with oxygen in the air, the atmosphere during firing is CO (g), CO ₂ (g), N _2.
It becomes a mixed gas of ₂ (g). At 1000 ° C. or higher, CO ₂ further reacts with coke to become CO, and this mixed gas atmosphere becomes a CO-containing reducing atmosphere. Therefore, in this case, the atmosphere around the molded body may remain air, and a CO-containing reducing atmosphere is generated during heating during firing.

On the other hand, the nitrogen-containing inert atmosphere is N
An atmosphere of _two gases alone or a mixed gas of N ₂ gas and another inert gas (argon, helium, etc.) can be used. Firing temperature is 1000-2000 ℃, preferably 1200-1500 ℃
Is suitable, and the firing time is usually 24 hours or longer, although it depends on the size of the molded product.

In the present invention, the compact to be fired contains Al powder. At the time of firing, this Al powder is C of the surrounding carbon raw material.
Reacts with aluminum carbide (Al
₄ C ₃ ). 4 Al (s) +3 C (s) → Al ₄ C ₃ (s) (1) When the firing atmosphere is a CO-containing reducing atmosphere, the Al ₄ C ₃ (s) produced by this reaction is It reacts with CO (g) to produce Al ₂ O ₃ (s). However, in reality, this reaction involves Al (g) generated by evaporation of Al powder. That is, Al ₄ C ₃ (s) is stable, and the partial pressure of Al (g) is the highest among the vapor phase species existing in equilibrium with Al ₄ C ₃ (s),
Al (g) and CO (g) react with each other to generate Al ₂ O ₃ (s). Since this reaction is a gas phase reaction, the reaction product Al ₂ O ₃ (s) is
The fibrous crystals are formed along the open pores, which are diffusion paths of the gas phase, and the open pores are effectively filled.

FIG. 1 shows the relationship between the partial pressure of CO gas generated by Al ₂ O ₃ (s) calculated thermodynamically and the temperature. The upper part of the equilibrium curve in the figure is the stable region of Al ₂ O ₃ (s). From this figure, for example, if the CO gas partial pressure is 10 ⁻³ (atm) or more at 1400 ° C., the Al ₂ O ₃ (s) ) Is stably generated. Therefore, in order to reduce open pores due to the formation of Al ₂ O ₃ , the CO gas partial pressure in the firing atmosphere should be selected so as to fall within the Al ₂ O ₃ stable region in this figure. However, the CO required for this
Since the lower limit of the gas partial pressure is as small as 10 ^-2 atm even at a firing temperature of 1600 ° C, it is sufficient if the CO gas content is 1% or more.

Al existing in equilibrium with Al ₄ C ₃ (s) as described above
As (g) reacts and is consumed, Al ₄ C ₃ (s) decomposes to supply Al (g), and finally the Al powder in the compact is Al ₄ C.
_{After 3} (s), it becomes a fibrous crystal of Al ₂ O ₃ (s) filling the open pores of the carbonaceous brick. However, among the Al powders, those adjacent to the open pores do not generate Al ₄ C ₃ (s) and are solid or liquid Al.
Reacts directly with N ₂ (g) and CO (g) in the atmosphere to form solid nitrides (AlN) and oxides (Al ₂ O ₃ ), which also fill the open pores. Of these, AlN finally reacts with CO (g) to produce Al ₂ O ₃ (s). Since metal Al has a relatively high vapor pressure, it is susceptible to the reactions involving Al (g) above and can effectively fill the pores, so it is possible to reduce not only the pore size but also the pore volume. It is supposed to be.

Even when the firing atmosphere is an N ₂ -containing inert atmosphere, that is, when CO is not included, the reaction of Al powder with C in the surrounding carbon raw material causes Al ₄ C ₃ (in accordance with the above formula (1)). s)
Is generated. However, in this case, AlN (s) is generated by the reaction of Al (g), which has the highest partial pressure among the vapor phase species existing in equilibrium with Al ₄ C ₃ (s), with N ₂ (g). However, since CO does not exist, AlN
(s) becomes the final product. That is, as in the case above, Al
Most of the powders pass through Al ₄ C ₃ (s) and become AlN (s) .Since the reaction of forming AlN (s) is a gas phase reaction, the generated AlN (s) is generated by the gas phase diffusion route. A fibrous crystal along some open pores,
The open pores are effectively filled. Also, the Al powder existing adjacent to the open pores does not generate Al ₄ C ₃ (s), but solid or liquid Al directly reacts with N ₂ (g) in the atmosphere to generate AlN (s). And fill the open pores.

When the firing atmosphere contains CO in addition to N ₂ , the produced AlN (s) reacts with CO as described above.
Although it changes to Al ₂ O ₃ (s), the generated Al ₂ O ₃ may form a solid solution with AlN and aluminum oxynitride may be generated. Therefore,
Filling the open pores of the carbonaceous brick obtained after firing by the method of the present invention is a fibrous aluminum oxide (Al ₂
O ₃ ), nitride (AlN), and either of these are solid solutions of aluminum oxynitride.

Since AlN has a thermal conductivity expansion coefficient closer to that of a graphite material than Al ₂ O ₃ , it does not impair the high thermal conductivity of carbonaceous bricks, and the expansion difference between the base material during heating and quenching is small. The tendency for cracks to occur is also reduced. In that sense, firing in an N ₂ -containing inert atmosphere, which fills the open pores with AlN, is preferable. However, as shown in the examples, C
The object of the present invention can be sufficiently achieved by firing in an O-containing reducing atmosphere and filling the open pores with Al ₂ O ₃ .

In any firing atmosphere, Al ₄ C ₃ produced as an intermediate during firing decomposes by reacting with moisture in the air at room temperature. Therefore, it is desirable to take a sufficient firing time so that Al ₄ C ₃ does not remain, but it is necessary to apply tar etc. to the surface of the carbonaceous brick after firing to prevent the ingress of water in the brick, so it is necessary. If so, take such action.

[0034]

The present invention will be described below in detail with reference to examples. In the examples,% and parts are by weight unless otherwise specified.
And parts by weight.

(Example 1) As a carbon raw material, a particle size range of 2 to
Using artificial graphite of 0.002mm alone, this carbon raw material 95%
And Al powder (average particle diameter 12 μm, purity 99.5%) 5% were mixed. To 100 parts of this powder mixture was added 10 parts of tar pitch as a binder and kneaded in an Erich mixer, and then using a hydraulic press, a diameter of 30 kg under a pressure of 800 kg / cm ^2.
It was formed into a cylindrical shape of mm × height 40 mm. This molded body,
Atmosphere with 100% CO gas flowing (CO gas partial pressure 1 at
In m), it was fired at 1400 ° C. for 24 hours to produce a carbonaceous brick.

The internal structure of the obtained carbonaceous brick was SEM
As a result of observation, the open pores in the brick were filled with fibrous crystals. In addition, this fibrous crystal is
It was confirmed to be ₂ O ₃ . This carbonaceous brick had a bulk density of 1.7 g / cm ³ , an apparent porosity measured according to JIS R 2205 of 10.2%, and a compression strength measured according to JIS R 2206 of 350 Kg / cm ² . Further, the alkali resistance and the hot metal erosion resistance of this carbonaceous brick were tested by the following method.

Alkali resistance test Alkali resistance was evaluated by a reaction test between potassium and carbonaceous bricks described in CAMP-ISIJ vol.6 (1993) -932. At this time, the brick sample temperature was 600 ° C., the atmosphere in the furnace was Ar, and it was held for 1 hour. The alkali resistance was evaluated by the expansion coefficient and appearance change of the sample taken out of the furnace after the test. Expansion rate is parallel to the molding direction (direction of the central axis of the cylinder)
It is the value obtained by dividing the coefficient of expansion by the length before the test.

Hot metal erosion resistance test A brick sample was placed in hot metal at 1500 ° C. under an argon atmosphere for 2 hours.
After soaking for a period of time, the remaining thickness of the samples was compared. The evaluation is represented by a hot metal erosion resistance index which is a relative value with the result of Example 1 being 100. The larger this value, the better the hot metal erosion resistance. The test results are summarized in Table 1 together with the production conditions of carbonaceous bricks and their characteristics.

(Example 2) A carbonaceous brick was produced in the same manner as in Example 1 except that the blending ratio of the powder mixture was changed to 80% artificial graphite and 20% Al powder.

Example 3 As the carbon raw material, the same artificial graphite as that used in Example 1 and roasted anthracite having a particle size of 0.3 mm or less were used. 70% artificial graphite, 25% roasted anthracite, and Al A carbonaceous brick was produced in the same manner as in Example 1 using a powder mixture containing 5% of powder.

(Comparative Example 1) A carbonaceous brick was prepared in the same manner as in Example 1, but the Al powder used had an average particle size of 30 μm and a purity of 95.5%.

(Comparative Example 2) Si powder (average particle size: 15 μm, purity: 99.5%) was used in place of the Al powder, and a carbonaceous brick was produced in the same manner as in Example 1 with the same mixing ratio. The test results and manufacturing conditions are also shown in Table 1.

[0043]

[Table 1]

Example 4 As a carbon raw material, a particle size range of 2 to
Artificial graphite of 0.002 mm and roasted anthracite with a grain size of 0.3 mm or less were used. 70% artificial graphite, 25% roasted anthracite, and Al powder
(Average particle size 15 μm, Purity 95.5%) To 100 parts of 5% powder mixture, add 10 parts of tar pitch as a binder and knead with an Eirich mixer. Then, using a hydraulic press, 800 kg / cm ² An atmosphere in which 230 × 114 × 65 mm parallel bricks were molded under the pressure of 100% N ₂ gas was passed.
In (N ₂ gas partial pressure 1 atm), it was fired at 1400 ° C. for 24 hours to produce a carbonaceous brick.

The internal structure of the obtained carbonaceous brick was SEM
As a result of observation, the open pores in the brick were filled with fibrous crystals. In addition, this fibrous crystal is
It was confirmed to be N. This carbonaceous brick has a bulk density of 1.74 g / cm ³ , an apparent porosity of 10.3% and a compressive strength of 370.
It was Kg / cm ² . Further, the bending strength measured according to JIS R 2213 is 160 Kg / cm ² , the thermal conductivity at room temperature and the linear expansion coefficient at 25 to 1000 ° C. measured by the laser flash method are 42 W / mK and It was 0.4%.

The carbonaceous bricks were further tested for alkali resistance and hot metal erosion resistance by the method described in Example 1.
The hot metal erosion resistance index in the following examples and comparative examples is shown as a relative value when the result in this example 4 is 100.

(Example 5) A carbonaceous brick was produced in the same manner as in Example 4 except that the blending ratio of the powder mixture was changed to 70% artificial graphite, 10% roasted anthracite, and 20% Al powder.

Example 6 A carbonaceous brick was produced in the same manner as in Example 4 except that the blending ratio of the powder mixture was changed to 25% artificial graphite, 70% roasted anthracite and 5% Al powder.

Comparative Example 3 A carbonaceous brick was produced in the same manner as in Example 4 except that the blending ratio of the powder mixture was changed to 70% artificial graphite and 30% roasted anthracite. That is, in this example,
No Al powder was added to the powder mixture.

(Comparative Example 4) The mixing ratio of the powder mixture was as follows: artificial graphite 70%, roasted anthracite 25% and Al powder (average particle size 30μ
m, purity 95.5%) A carbonaceous brick was produced in the same manner as in Example 4 except that the content was changed to 5%.

Table 2 shows the test results and manufacturing conditions of the carbonaceous bricks obtained in Examples 4 to 6 and Comparative Examples 3 to 4 described above.

[0052]

[Table 2]

As is clear from Tables 1 and 2, in Comparative Examples 2 and 3 in which carbonaceous bricks were produced by a conventional method without adding Al powder, the apparent porosity of the bricks was 17.4 to 18.4%.
However, it was also inferior in alkali resistance, and cracks occurred in the bricks in the alkali resistance test, and the expansion rate at that time was as large as 1.2%.

On the other hand, according to the present invention, a carbonaceous brick obtained by blending a carbon raw material with fine Al powder having an average particle size of 22 μm or less and firing it in an atmosphere containing CO or N ₂ is
The apparent porosity was as small as 11% or less, the alkali resistance was remarkably improved, the brick appearance did not change in the alkali resistance test, and the expansion coefficient was very low, less than 0.3%. Also, N ₂
When fired in an atmosphere, the material filling the open pores was AlN, so the strength and thermal properties were also improved.

However, even if Al powder is blended with the carbon raw material,
When the average particle diameter of the Al powder exceeds 25 μm, as shown in Comparative Examples 1 and 4, although the apparent porosity is lowered, the alkali resistance is not sufficiently improved, and the expansion coefficient is still large. In addition, when Si powder was mixed instead of Al powder, Comparative Example 2 was used even if the average particle diameter was 25 μm or less.
As shown in Table 1, the apparent porosity and the alkali resistance are the same as those of Comparative Example 3 in which the metal powder is not mixed, and it can be seen that the Si powder is not effective at all.

From the above, according to the present invention, alkali resistance, which is a drawback of conventional carbonaceous bricks, is improved, and other properties such as strength, thermal properties, and hot metal erosion resistance are maintained at the same level. Slightly improved. Therefore, by using the carbonaceous brick of the present invention for lining the bottom of the blast furnace,
The life of the blast furnace can be remarkably extended.

[Brief description of drawings]

FIG. 1 is a diagram showing a stable region of Al ₂ O ₃ (s) as a relationship between CO gas partial pressure and temperature.

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Claims (3)

[Claims] 1. An open porosity partially filled with fibrous aluminum oxide and / or nitride crystals, having an apparent porosity of 11% or less and an expansion coefficient in an alkali resistance test of 0.5 or less, low. Carbonaceous brick for blast furnace with high porosity and excellent alkali resistance. 2. After kneading and molding a mixture containing one or more carbon raw materials, metallic aluminum powder having an average particle size of 25 μm or less, and an organic binder, in a CO-containing reducing atmosphere or a nitrogen-free atmosphere. A method for producing a carbonaceous brick for a blast furnace, which has a low porosity and is excellent in alkali resistance, which is characterized by firing in an active atmosphere. 3. The blending amount of the metallic aluminum powder is 0.1 to 10 based on the total amount of the carbon raw material and the metallic aluminum powder.
The method according to claim 2, which is in the range of 20 wt%.